1. Field of the Invention
The present invention relates to a focusing system in an optical apparatus such as photographic camera. More particularly, the present invention relates to a type of focusing system in which selection can be made between automatic focusing by the operation of an autofocusing device and manual focusing by a manual operation.
2. Description of the Prior Art
One type of an autofocusing apparatus known in the art has set distance signal forming means interlocked with a lens to be focused and disposed to form a set distance signal corresponding to the value of distance set for the lens, distance detecting means for detecting object distance and forming a detected distance signal corresponding to the detected distance, comparing means for comparing said set distance signal with said detected distance signal to produce a comparison output and driving means for driving the lens for focal adjustment. To achieve the automatic focusing, the lens is moved until the detected distance signal becomes coincident with the set distance signal.
As readily understood, distance detecting means used in this type of apparatus has usually a limitation of its ability to detect distance. Therefore, when such autofocusing device is used, for example, in an optical apparatus such as photographic camera, it is desirable to cover the limited automatic focusing ability by manual focusing. In this case, the range set for manual focusing is beyond the range within which the autofocusing device is effective. Within the manual focusing range one can carry out focusing manually at his own will. In such an autofocusing devices, its effective range for automatic focusing is from 1.0 m to .infin.. In contrast, for instance, in the case of single lens reflex camera, its taking lens has a distance adjustable range ranging from 0.5 m to .infin.. In this instance, since the autofocusing range allowable for the taking lens is limited to 1.0 m-.infin., it is desirable to provide a manual focusing range covering the range of 0.5 m to .infin.. By doing so, it is possible to adjust the focus of the taking lens up to its own limit (in this case, its limit on the minimum distance side is 0.5 m) at least employing the manual focusing.
However, the use of combination of automatic focusing and manual focusing mentioned above brings forth a problem, in particular, when such a manual focusing range beyond the limited automatic focusing range is set in the aforementioned type of focusing system provided with an autofocusing device. The problem is that the automatic focusing of the optical system within the automatic focusing range by the autofocusing device should be when autofocusing start means is operated, irrespective of the position of the optical system, at once within the manual focusing range. Otherwise, the focusing system will be inconvenience to the user. In the system according to the prior art, the automatic focusing of the optical system by the autofocusing device can be effected at once when said autofocusing start means is operated, so long as the manually adjusted position of the optical system is within the automatic focusing range. However, if the position of the optical system is out of the automatic focusing range, automatic focusing of the optical system can not be effected at once. However, it will occur after the user has manually returned the optical system to a position within the automatic focusing range. This operation, i.e. a switch-over operation is troublesome to the user.